Ghd8 controls rice photoperiod sensitivity by forming a complex that interacts with Ghd7

BACKGROUND: Flowering time is one of the most important agronomic characteristics that ultimately determine yield potential and eco-geographical adaptation in crops. Ghd8 and Ghd7, two major flowering genes, have similar functions and large pleiotropic effects in controlling the heading date, plant height and grain yield of rice. However, these gene interactions at the genetic and molecular levels have not been determined to date. RESULTS: In this study, we investigated the genetic interaction between Ghd8 and Ghd7 by using a set of near-isogenic lines and a panel of natural germplasm accessions in rice. We found that Ghd8 affected multiple agronomic traits in a functional Ghd7-dependent manner. Both functional Ghd8 and Ghd7 are pivotal for rice photoperiod sensitivity controlled by Hd1 and Hd3a. GHD8 could form a heterotrimeric complex with HD1 and OsHAP5b to activate the transcription of Ghd7 by binding directly to the promoter region of Ghd7, which contains the CCAAT-box motif. CONCLUSIONS: The results of this study help to elucidate the genetic and molecular bases of Ghd8 and Ghd7 interactions, indicating that Ghd8 acts upstream of Ghd7 to activate its transcription, which inhibits Hd3a expression and thus affects flowering time and rice adaptation.